WASHINGTON — The Air Force has grounded its fleet of enormous C-5 Galaxy cargo planes based at Dover Air Force Base following a second malfunction of a plane’s nose landing gear in the last two months, the service announced Tuesday.

The stand-down of the Delaware base’s C-5s was ordered Monday by Air Force Gen. Carlton Everhart II, commander of Air Mobility Command, who cited safety concerns. The order only impacts the 18 C-5 aircraft – twelve primary and six backup planes – based at Dover.

The Air Force has 56 C-5s across the service.

“Aircrew safety is always my top priority and is taken very seriously,” Everhart said in a prepared statement. “We are taking the appropriate measures to properly diagnose the issue and implement a solution.”

Neither incident resulted in injuries to any personnel, said Air Force Maj. Korry Leverett, a spokesman for Air Mobility Command. Both malfunctions occurred during landing at Naval Station Rota in Spain. They occurred May 22 and July 15, Leverett said.

It was not clear how much damage the malfunctions caused to either plane or to the runways at Rota. Leverett said the Air Force is investigating the incidents.

The service is also conducting inspections to ensure all of the Dover-based C-5 nose landing gears were operating properly. It was not clear how long the inspections would take or when the stand-down might be lifted.

Air Mobility Command “will work to ensure worldwide mission requirements are minimally impacted,” the statement read.

The Lockheed Martin-built C-5 Galaxy is the largest airplane in the Air Force’s inventory and among the most massive jets in the world. The 65-foot tall, 247-foot long aircraft can carry up to 270,000 pounds, according to an Air Force fact sheet.

It can carrying any of the Army’s air-transportable equipment, including up to two M1 main battle tanks or up to six AH-64 Apache attack helicopters. It can also carry 81 combat-equipped troops alongside 36 standard size pallets loaded with gear, according to the Air Force.